1. Field of the Invention
This invention relates to automatic fuel ignition systems, and more particularly, to an automatic fuel ignition system employing electronic leak detection for valves.
2. Description of The Prior Art
Automatic fuel ignition systems include a control circuit which provides sequential operation of valves of the system. For example, in pilot ignition systems, the control circuit responds to a request signal, typically the application of power to the control circuit in response to operation of a thermostatically-controlled switch, to effect the operation of a pilot valve to supply fuel to a pilot outlet. The control circuit also enables an ignition circuit to generate ignition sparks for igniting the fuel to establish a pilot flame. When a pilot flame is established, the control circuit operates a main valve which supplies fuel to a main burner for ignition by the pilot flame.
In such systems, conditions, such as the presence or absence of a flame at the pilot outlet or the main burner, are frequently used to effect the sequencing operations provided by the control circuit and to enable various checks to assure fail-safe operation of the system to prevent inadvertant operation of the valves. Thus, a leak condition for either the pilot valve or the main valve, could interrupt the normal sequencing operations of the system as well as inhibiting certain of the checks which afford fail-safe operation of the system. Morever, in the event either the pilot valve or the main valve is leaking, fuel will be continuously supplied to the pilot outlet of the main burner, wasting fuel and producing a potentially hazardous condition.
In the U.S. Pat. No. 3,840,322 of Philip J. Cade, there is disclosed electrical control circuitry for use in an automatic fuel ignition system and which is operable to effect lock out of the system whenever a flame is provided at a burner apparatus prior to the operation of a fuel valve of the system. Such operation is effected by delaying the energization of the pilot valve for a pre-ignition delay interval after the system is activated. During such time, a lock out switch is energized. If a flame is detected by a flame sensing circuit during the pre-ignition delay, the delay timer is inhibited and the lock out switch continues to be energized and effects irreversible lock out of the system after a predetermined time. Accordingly, it would appear that in the event of a line voltage interruption of a very short duration, wherein the pilot flame may not be extinguished before power is restored, the flame sensing circuit would inhibit the pre-ignition delay timer and permit the system to be locked out. Also, for a loss of flame after the establishment of normal operation, the ignition sequence cannot be reinitiated, and the system proceeds to lock out status. For such conditions, manual reset of the system is required before the system can be reactivated, even though the valves may be functioning properly.
Therefore, it would be desirable to have an automatic fuel ignition system which automatically distinguishes between a leak condition for a pilot valve of the system and a momentary line voltage interruption and which permits recycling of the system following a momentary power loss or a flame out condition, but effects shut down of the system for a leak condition for the valve.